Improve coverage for init false attributes (#486)

* Improve coverage for init false attributes

* One more test for coverage

* Some more coverage, update Pendulum

* Speed up heterogenous tuple unstructuring

* More init=False tests

Author: Tinche

Diff for: .github/workflows/main.yml

@@ -71,7 +71,7 @@ jobs:
           echo "total=$TOTAL" >> $GITHUB_ENV
 
           # Report again and fail if under the threshold.
-          python -Im coverage report --fail-under=97
+          python -Im coverage report --fail-under=98
 
       - name: "Upload HTML report."
         uses: "actions/upload-artifact@v3"

Diff for: HISTORY.md

@@ -15,6 +15,8 @@ Our backwards-compatibility policy can be found [here](https://github.com/python
   Previously this behavior was underspecified and inconsistent, but followed this rule in the majority of cases.
   Reverting old behavior is very dependent on the actual case; ask on the issue tracker if in doubt.
   ([#473](https://github.com/python-attrs/cattrs/pull/473))
+- **Minor change**: Heterogeneous tuples are now unstructured into tuples instead of lists by default; this is significantly faster and widely supported by serialization libraries.
+  ([#486](https://github.com/python-attrs/cattrs/pull/486))
 - Introduce {meth}`BaseConverter.get_structure_hook` and {meth}`BaseConverter.get_unstructure_hook` methods.
   ([#432](https://github.com/python-attrs/cattrs/issues/432) [#472](https://github.com/python-attrs/cattrs/pull/472))
 - Introduce the [_msgspec_](https://jcristharif.com/msgspec/) {mod}`preconf converter <cattrs.preconf.msgspec>`.

Diff for: docs/defaulthooks.md

@@ -194,6 +194,7 @@ Any type parameters set to `typing.Any` will be passed through unconverted.
 (1, '2', 3.0)
 ```
 
+When unstructuring, heterogeneous tuples unstructure into tuples since it's faster and virtually all serialization libraries support tuples natively.
 
 ### Deques
 

Diff for: pdm.lock

@@ -1054,7 +1054,7 @@ def gen_unstructure_hetero_tuple(
         self, cl: Any, unstructure_to: Any = None
     ) -> HeteroTupleUnstructureFn:
         unstructure_to = self._unstruct_collection_overrides.get(
-            get_origin(cl) or cl, unstructure_to or list
+            get_origin(cl) or cl, unstructure_to or tuple
         )
         h = make_hetero_tuple_unstructure_fn(cl, self, unstructure_to=unstructure_to)
         self._unstructure_func.register_cls_list([(cl, h)], direct=True)

Diff for: src/cattrs/converters.py

@@ -372,7 +372,8 @@ def make_dict_structure_fn(
                 )
 
             struct_handler_name = f"__c_structure_{an}"
-            internal_arg_parts[struct_handler_name] = handler
+            if handler is not None:
+                internal_arg_parts[struct_handler_name] = handler
 
             ian = a.alias
             if override.rename is None:
@@ -391,7 +392,7 @@ def make_dict_structure_fn(
                 i = f"{i}  "
                 type_name = f"__c_type_{an}"
                 internal_arg_parts[type_name] = t
-                if handler:
+                if handler is not None:
                     if handler == converter._structure_call:
                         internal_arg_parts[struct_handler_name] = t
                         pi_lines.append(
@@ -511,7 +512,7 @@ def make_dict_structure_fn(
             allowed_fields.add(kn)
 
             if not a.init:
-                if handler:
+                if handler is not None:
                     struct_handler_name = f"__c_structure_{an}"
                     internal_arg_parts[struct_handler_name] = handler
                     if handler == converter._structure_call:
@@ -803,7 +804,7 @@ def make_mapping_structure_fn(
     val_type=NOTHING,
     detailed_validation: bool = True,
 ) -> MappingStructureFn[T]:
-    """Generate a specialized unstructure function for a mapping."""
+    """Generate a specialized structure function for a mapping."""
     fn_name = "structure_mapping"
 
     globs: dict[str, type] = {"__cattr_mapping_cl": structure_to}

Diff for: src/cattrs/gen/__init__.py

@@ -1,10 +1,11 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Any, Callable
+from typing import TYPE_CHECKING, Any
 
 from attrs import NOTHING, Attribute, Factory
 
 from .._compat import is_bare_final
+from ..dispatch import StructureHook
 from ..fns import raise_error
 
 if TYPE_CHECKING:  # pragma: no cover
@@ -13,7 +14,7 @@
 
 def find_structure_handler(
     a: Attribute, type: Any, c: BaseConverter, prefer_attrs_converters: bool = False
-) -> Callable[[Any, Any], Any] | None:
+) -> StructureHook | None:
     """Find the appropriate structure handler to use.
 
     Return `None` if no handler should be used.

Diff for: src/cattrs/gen/_shared.py

@@ -0,0 +1,31 @@
+"""Tests for collections in `cattrs.gen`."""
+from typing import Generic, Mapping, NewType, Tuple, TypeVar
+
+from cattrs import Converter
+from cattrs.gen import make_hetero_tuple_unstructure_fn, make_mapping_structure_fn
+
+
+def test_structuring_mappings(genconverter: Converter):
+    """The `key_type` parameter works for generics with 1 type variable."""
+    T = TypeVar("T")
+
+    class MyMapping(Generic[T], Mapping[str, T]):
+        pass
+
+    def key_hook(value, _):
+        return f"{value}1"
+
+    Key = NewType("Key", str)
+
+    genconverter.register_structure_hook(Key, key_hook)
+
+    fn = make_mapping_structure_fn(MyMapping[int], genconverter, key_type=Key)
+
+    assert fn({"a": 1}, MyMapping[int]) == {"a1": 1}
+
+
+def test_unstructure_hetero_tuple_to_tuple(genconverter: Converter):
+    """`make_hetero_tuple_unstructure_fn` works when unstructuring to tuple."""
+    fn = make_hetero_tuple_unstructure_fn(Tuple[int, str, int], genconverter, tuple)
+
+    assert fn((1, "1", 2)) == (1, "1", 2)

Diff for: tests/test_gen_collections.py

@@ -2,7 +2,7 @@
 from typing import Dict, Type
 
 import pytest
-from attrs import NOTHING, Factory, define, field
+from attrs import NOTHING, Factory, define, field, frozen
 from hypothesis import assume, given
 from hypothesis.strategies import data, just, one_of, sampled_from
 
@@ -450,12 +450,18 @@ class A:
 def test_init_false_overridden(converter: BaseConverter) -> None:
     """init=False handling can be overriden."""
 
+    @frozen
+    class Inner:
+        a: int
+
     @define
     class A:
         a: int
         b: int = field(init=False)
         _c: int = field(init=False)
-        d: int = field(init=False, default=4)
+        d: Inner = field(init=False)
+        e: int = field(init=False, default=4)
+        f: Inner = field(init=False, default=Inner(1))
 
     converter.register_unstructure_hook(
         A, make_dict_unstructure_fn(A, converter, _cattrs_include_init_false=True)
@@ -464,28 +470,36 @@ class A:
     a = A(1)
     a.b = 2
     a._c = 3
+    a.d = Inner(4)
 
-    assert converter.unstructure(a) == {"a": 1, "b": 2, "_c": 3, "d": 4}
+    assert converter.unstructure(a) == {
+        "a": 1,
+        "b": 2,
+        "_c": 3,
+        "d": {"a": 4},
+        "e": 4,
+        "f": {"a": 1},
+    }
 
     converter.register_structure_hook(
-        A,
-        make_dict_structure_fn(
-            A,
-            converter,
-            _cattrs_include_init_false=True,
-            _cattrs_detailed_validation=converter.detailed_validation,
-        ),
+        A, make_dict_structure_fn(A, converter, _cattrs_include_init_false=True)
     )
 
-    structured = converter.structure({"a": 1, "b": 2, "_c": 3}, A)
+    structured = converter.structure({"a": 1, "b": 2, "_c": 3, "d": {"a": 1}}, A)
     assert structured.b == 2
     assert structured._c == 3
-    assert structured.d == 4
+    assert structured.d == Inner(1)
+    assert structured.e == 4
+    assert structured.f == Inner(1)
 
-    structured = converter.structure({"a": 1, "b": 2, "_c": 3, "d": -4}, A)
+    structured = converter.structure(
+        {"a": 1, "b": 2, "_c": 3, "d": {"a": 5}, "e": -4, "f": {"a": 2}}, A
+    )
     assert structured.b == 2
     assert structured._c == 3
-    assert structured.d == -4
+    assert structured.d == Inner(5)
+    assert structured.e == -4
+    assert structured.f == Inner(2)
 
 
 def test_init_false_field_override(converter: BaseConverter) -> None:
@@ -538,6 +552,29 @@ class A:
     assert structured.d == -4
 
 
+def test_init_false_no_structure_hook(converter: BaseConverter):
+    """init=False attributes with converters and `prefer_attrs_converters` work."""
+
+    @define
+    class A:
+        a: int = field(converter=int, init=False)
+
+    converter.register_structure_hook(
+        A,
+        make_dict_structure_fn(
+            A,
+            converter,
+            _cattrs_prefer_attrib_converters=True,
+            _cattrs_include_init_false=True,
+        ),
+    )
+
+    res = A()
+    res.a = 5
+
+    assert converter.structure({"a": "5"}, A) == res
+
+
 @given(forbid_extra_keys=..., detailed_validation=...)
 def test_forbid_extra_keys_from_converter(
     forbid_extra_keys: bool, detailed_validation: bool